Practice Essentials

Acute intermittent porphyria (AIP) is one of the porphyrias, a group of hereditary diseases that involve defects in heme metabolism and result in excessive secretion of porphyrins and porphyrin precursors.
[1] AIP manifests as episodes of abdominal pain, neuropathies, and constipation, but, unlike most types of porphyria, patients with AIP do not have a rash.

The diagnosis of AIP can be confirmed by finding an elevated level of porphobilinogen (>6 mg/L) on a spot urine test during an acute attack (see Workup). High doses of glucose can inhibit heme synthesis and are useful for treatment of mild attacks. Patients experiencing severe attacks, especially those with severe neurologic symptoms, should be treated with hematin. During attacks, which generally last for several days, patients require symptomatic treatment for pain and other manifestations. (See Treatment and Medication.)

Pathophysiology

AIP is an autosomal dominant disease that results from defects in the enzyme porphobilinogen-deaminase. This enzyme speeds the conversion of porphobilinogen to hydroxymethylbilane. In AIP, the porphyrin precursors, porphobilinogen and amino-levulinic acid (ALA), accumulate. The predominant problem appears to be neurologic damage that leads to peripheral and autonomic neuropathies and psychiatric manifestations.
[2]

Although levels of porphobilinogen and ALA are always elevated during acute attacks, how this leads to the symptomatic disease is still unclear because most patients with the genetic defect have excessive porphyrin secretion but no symptoms.

A case-control study in 50 patients by Storjord et al found evidence that AIP is associated with systemic inflammation. Levels of prealbumin, C-peptide, and insulin, along with measures of kidney function, were all decreased in symptomatic patients, but not in asymptomatic ones. The decrease in C-peptide levels in symptomatic AIP cases indicates that reduced insulin release is associated with enhanced disease activity and reduction in kidney function.
[3]

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Epidemiology

Frequency

United States

Estimates vary from 1-5 cases per 100,000 population.

International

European studies indicate that the prevalence of AlP is approximately five per 100,000 population.
[4] The prevalence can be as high as 60-100 cases per 100,000 population in northern Sweden.

Sex- and Age-related Demographics

In most series, AIP affects women more than men, with a ratio of 1.5-2:1.

Most patients become symptomatic at age 18-40 years. Attacks occurring before puberty or after age 40 years are unusual unless a major provocation, such as new use of phenobarbital or estrogens, had occurred.